Method for isolating aleurone particles

ABSTRACT

The invention relates to a method and device for separating a mixture, made of particles of a first particle type and a second particle type, especially aleurone particles and shell particles made of comminuted bran, said particles being scarcely distinguishable in terms of size and density, into various types of particles. Separation occurs according to particle-type specific triboelectric charging of said particles in a first active area and subsequent separation of the differently charged moving particles in an electric field.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of International Application No.PCT/CH02/00547, filed Oct. 2, 2002 and German Application No. 101 54462.6, filed Nov. 8, 2001, the complete disclosures of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The invention relates to a method and a device for separating thevarious sorts of particles in a mixture comprised of particles producedby comminuting the grains of cereal grains, in particular wheat, and arepresent as a mixture consisting of at least a first and second sort ofparticle. In addition, the invention relates to a product which is alsoobtained via the method and device according to the invention.

b) Description of the Related Art

WO 85/04349 describes a method for obtaining aleurone cell particlesfrom wheat gain. In this case, the grain particles are comminuted in ahammer mill in a first step, so that aleurone cell particles and shellparticles are present as a mixture. This mixture is given an electricalcharge through exposure to frictional electricity in a second step,wherein the aleurone cell particles and the shell particles receivedifferent electrostatic charges. In a third step, the mixture with thedifferently charged particles is moved through an electrical field, sothat the differently charged particles are varyingly deflected, whereinthe shell particles and aleurone cell particles are caught in separatecontainers. The frictional electric charge (step 2) takes place in astream of dry air, into which the mixture is introduced, and which movesin a hollow column. In this case, obviously turbulent air streams arisein the column (“elutriator”), wherein the particles in the mixture rubagainst both each other and the interior wall of the elutriator, therebyreceiving the respective electrostatic charge.

In this method of prior art, however, large quantities of air had to bemoved. Nonetheless, no intensive frictional electric interaction takesplace between the particles and the interior elutriator walls.

OBJECT AND SUMMARY OF THE INVENTION

Therefore, the primary object of the invention is to separate a mixturecomprised of various sorts of particles, in particular aleurone andshell particles from comminuted grain, which hardly differ in terms ofsize and density, into its various sorts of particles more efficientlythan in prior art.

This object is achieved by a method in which:

-   -   a) The particles of the first particle sort and second particle        sort in the mixture are moved along at least one surface of at        least one solid material in a first impact area in such a way as        that at least one portion of their particle surface is at least        sectionally in contact with the solid material surface as they        move along the at least one solid material surface, as a result        of which the particles of the first particle sort and the        particles of the second particle sort become electrically        charged in such a way that the electrical charge of the        particles of the first particle sort differs from the electrical        charge of the particles of the second particle sort enough to        enable an electrostatic separation of particles of the first        particle sort from particles of the second particle sort;    -   b) in a second impact area, the particles of the first particle        sort and second particle sort with the sufficiently different        electrical charges are subsequently moved into an electrical        field between a first electrode area and a second electrode        area, between which there is an electrical potential difference,        at essentially the same velocity, as a result of which the        particles of the first particle sort and second particle sort        with the sufficiently different electrical charges move along        sufficiently different paths as they travel through the        electrical field; and    -   c) the particles of the first particle sort and the particles of        the second particle sort are caught at a first location and at a        second location at the end of their journey through the        electrical field, characterized in that the at least one surface        of the at least one solid material is concave in the first        impact area, and that the particles of the first sort and        particles of the second sort in the mixture moving along the        concave surface are pressed against the concave surface of the        solid material as a result of their centrifugal force as they        move inside the first impact area.

The particles can be gathered at this first and second location, andremoved after enough have accumulated. As an alternative, they can alsobe continuously, e.g., pneumatically, conveyed further in step c) afterseparation in step b), and then be routed to a packaging system, forexample.

In particular, the particles of the first particle sort are aleuroneparticles, and the particles of the second particle sort are residualparticles from which aleurone has been removed, in particular shellparticles, of the comminuted grain.

The object according to the invention is also achieved with a deviceaccording to the invention, with:

-   -   a) a first impact area with at least one surface of at least one        solid material, along which the particles of the first particle        sort and the second particle sort of the mixture can move in        such a way that at least one portion of their particle surface        is at least sectionally in contact with the solid material        surface as they move along the at least one solid material        surface; and    -   b) a second impact area subsequent to the first impact area,        with a first electrode area and a second electrode area, between        which an electrical voltage can be applied; and with a first        accumulation area for particles of the first sort and an        accumulation area for particles of the second sort separate from        the first accumulation area, characterized in that the at least        one surface of the at least one solid material is concave in the        first impact area, so that the particles of the first sort and        second sort that can move along the concave surface are pressed        against the concave surface of the solid material as a result of        their centrifugal force as they move inside the first impact        area.

In particular, the at least one surface of the at least one solidmaterial is concave in the first impact area, so that the particles ofthe first sort and second sort that can move along the concave surfaceare pressed against the concave surface of the solid material as aresult of their centrifugal force as they move inside the first impactarea.

The product according to the invention, in particular aleuroneparticles, which was obtained by separating the various particle sortsof the mixture through the use of steps a), b) and c) of theaforementioned method, has a high level of purity.

It is preferably obtained through the repeated application of steps a),b) and c).

Additional advantages, features and possible applications of theinvention will be presented in the following description of twoexemplary embodiments of the invention based on the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a first exemplary embodiment of the invention; and

FIG. 2 shows a second exemplary embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first device according to the invention shown on FIG. 1 comprises asupply vessel 22 in which the mixture 1 to be separated, which containsat least a first particle sort 2 and a second particle sort 3, is routedto the first impact area 13, 14, in which particles 2, 3 of mixture 1are given an electrical charge varying by particle sort before theparticles 2, 3 carrying different electric charges are supplied to thesecond treatment area 31, 32, 35, where they accumulate at differentlocations 33, 34 in a separation vessel 35, sorted according to type ofparticle based on their electric charge.

Through the force of gravity, the mixture 1 goes out of the feed vessel22, which tapers toward the bottom, into a conveyor device 18, 19consisting of a conveyor screw 18 and into a conveyor channel 19. Theconveyor screw 18, which is driven by a drive motor 23, conveys themixture 1 through a product inlet 15 into a housing 14, where a rotorelement 13 is rotatably mounted.

There is a gap area 21 between the rotor element 13, which is driven bya drive motor 24, and the housing 14, such that the mixture 1, which issupplied through the product inlet 15 and strikes the rotor element 13,is accelerated both radially and tangentially through this gap area dueto friction at the surface of the rotor element. The mixture 1accelerated in this way passes through the gap area 21 and obliquelystrikes the surface 11 of the inside wall of the housing, which has aconcave curvature. Due to its own inertia (centrifugal force) and due toconstantly resupplied mixture, the mixture 1 is pressed against thesurface 11 having a concave curvature and is conveyed along this surfaceuntil it comes out of the housing 14 through the product outlet 16 andenters a separation vessel 35.

The disk-shaped rotor element 13 has elevations 20, which are situatedon its disk surface facing the product inlet 15. In addition to theabove-mentioned friction on the surface of the rotor element 13 (“baffledisk”), these elevations 20 also contribute toward the acceleration ofthe mixture 1 and the ever-present air through the gap area 21, and onthe other hand, they also exert an impact effect (baffle effect) on theparticles 2, 3 of the mixture, so that any agglomerates of multipleparticles which might be present are broken up. This impact separation(baffle separation) of agglomerates before or during the buildup ofelectric charge on the particles due to friction on the solid bodysurfaces is important, because such agglomerates may of course alsoconsist of particles of different types, which would then reach thecollecting site 33 or at the collecting site 34, depending on theirtotal charge. Then, however, in any case one would have “foreignparticles” at the respective collecting sites 33 and 34.

Depending on their geometric shapes, these elevations 20 may haveprimarily an accelerating and/or pumping effect on the mixture and/orthe air, or they may have primarily a dispersing effect on the particlesof the mixture. A blocky, angular shape of these elevations 20 promotesa dispersing effect, while a paddle shape increases the acceleration orpumping effect. Elevations of different shapes may also be provided onthe rotor element 13 to achieve a controlled effect.

To prevent the mixture 1, which is supplied through the product inlet15, from traveling even a very short distance through the gap area 21between the product inlet 15 and the product outlet 16 and therebyescaping the necessarily intense action in the first treatment area 13,14, the product inlet 15 is situated eccentrically with respect to therotor element 13. In addition (and not for reasons of betterillustration as in FIG. 1), the product inlet 15 is situated directlybehind the product outlet 16 in the direction of rotation of the rotorelement 13 peripherally, so that the mixture travels at leastapproximately 360° on a spiral pathway in the gap area 21 between theproduct inlet 15 and the product outlet 16. This prevents“short-circuiting” of the pathway of the mixture between the productinlet and the product outlet.

During its path through the gap area 21, the particles 2, 3 of themixture 1 come in intense contact with the inside surfaces 11, 12 of thehousing 14 and with the surface of the rotor element 13, in particularits elevations 20 and the concave curvature of the inside surface 11 ofhousing 14. This leads to a specific electric charge buildup on theparticles of the different types of particles 2, 3.

Because of their high velocity, the dispersed particles coming outthrough the product outlet 6 go approximately horizontally into theseparation vessel 35, whereby the cylindrical neck area 35 a of theseparation vessel serves as a calming zone for the particles carryingdifferent electric charges as they come out of the housing 14. They thensettle out in the interior of the separation vessel under the influenceof gravity. In the interior of the separation vessel 35, there is afirst electrode 31 and a second electrode 32 opposite it. The firstelectrode 31 is grounded by a line 38, which contains a voltage source37, while the second electrode 32 is grounded directly via a line 39.The differently charged particles settling out in the electric fieldbetween the two electrodes 31 and 32 travel downward on different paths,depending on their electric charge. A partition 36, which projects fromthe bottom area 35 b of the collecting vessel 35 into the electric fieldbetween the electrodes 31, 32 subdivides the lower interior space of theseparation vessel 35 into a first collecting area 33 and a secondcollecting area 34 in which the particles of the first type and/or theparticles of the second type are collected.

In an advantageous modification of this first exemplary embodiment fromFIG. 1, an air classification is also performed in the first treatmentarea 13, 14. To this end, air or another gas mixture is pumped throughan air inlet (not shown) into the first treatment area 13, 14 and isguided within the first treatment area 13, 14 so that the fines (“flour”from endosperm residues, optionally still adhering to the aleuroneparticles) are separated from the coarse fraction (pure aleuroneparticles and pure husk particles), the fines being removed with the airstream through an air outlet (not shown) and only the coarse fractionpassing through the product outlet 16 into the second treatment area 31,32, 35.

The second device according to this invention as shown in FIG. 2 differsfrom that shown in FIG. 1 in its first treatment area. Otherwise all theelements are identical and carry the same reference notation as those inFIG. 1. Instead of the housing 14 with the rotor element 13 which isrotatably mounted on it and can be driven by the drive motor 24, thedevice in FIG. 2 has a curved channel with a first end 27 a and a secondend 27 b. The mixture 1 coming from a feed vessel 22, in particularaleurone particles and husk particles of the bran, is supplied through aproduct inlet 15, and a moving fluid, in particular air, is suppliedthrough a fluid inlet 29 to a fluidization area 17 at the end of whichthere is a dispersion angle 26, which is connected to the first end 27 aof the curved channel 27 and through which the fluidization area 17opens into the curved channel 27. The second end 27 b of the curvedchannel 27 opens into a product separator 28 with a fluid outlet 30 anda product outlet 16, which opens into the separation vessel 35.

The conveyor device 18, 19 transports the mixture 1 out of the feedvessel 22, through the product inlet 15 and into the fluidization area17. A sufficient amount of fluid at a sufficient velocity is used toachieve airborne conveyance without any accumulation of particles in theinterior of the curved channel 27. Due to the abrupt deflection when theparticles impact on the dispersing angle 26, the above-mentioneddispersion/de-agglomeration of the particles of the mixture isaccomplished. During their subsequent movement in the fluid stream anddue to the friction between the particles moving along the insidesurface of the curved channel 27, there is a particle type-specificbuildup of electric charge on the particle types 2, 3 of mixture 1. Thefluid is separated through the fluid outlet 30 in the downstream productseparator 28, and the mixture of the differently charged particlesaccording to type of particle then enters the separation vessel with itselectric field.

In principle, two cases of electric charging of the particles can bedifferentiated:

The particles of the first type of particle are negatively (positively)charged and the particles of the second type of particle are negatively(positively) charged, but to a different extent. These particles thusdiffer only in the absolute value of their charge, but not in thepolarity of the charge.

The particles of the first type of particle are negatively (positively)charged and the particles of the second type of particle are positively(negatively) charged. The particles thus differ in polarity and possiblyalso in the absolute value of their charge.

In the first case, the electrically charged particles of the first typeand those of the second type repel one another, and there is practicallyno re-agglomeration of different particles. Separation takes place inthe electric field due to different amounts of deflection in the samedirection.

In the second case, the electrically charged particles of the first typeand those of the second type attract one another and re-agglomeration ofdifferent particles is possible. Separation takes place in the electricfield due to different amounts of deflection in opposite directions.

To prevent re-agglomeration of particles in any case before they areseparated into the different types of particles in the electric field,the “particle densities” must be kept low and the “particle dwell times”must be kept short during the buildup of electric charge in the firsttreatment area accordingly.

In the first exemplary embodiment in FIG. 1, this is accomplishedbecause of the selected geometry due to the cross section of the gaparea, which becomes wider in the radial direction, and due to asufficiently high rotational speed of the rotor element 13.

In the second exemplary embodiment in FIG. 2, this is accomplished byadjusting a sufficiently low product throughput/fluid throughput ratioin the fluidization area 17 and a sufficiently high fluid velocity.

In all the exemplary embodiments of the device according to thisinvention, the type of particle and the type of solid material on whichthe particles develop a triboelectric charge play a significant rolewhether the first case or the second case is obtained.

Thus, for example, very good charge buildup and separation results wouldbe achieved for an aleurone particle/husk particle mixture if the solidsurfaces 11 and 12, which play a crucial role in the charge buildup, aremade of stainless steel.

While the foregoing description and drawings represent the presentinvention, it will be obvious to those skilled in the art that variouschanges may be made therein without departing from the true spirit andscope of the present invention.

List of Reference Notation

-   1 mixture of particles-   2 first type of particle-   3 second type of particle-   11 first surface (concave)-   12 additional surface-   13, 14 first treatment area (first exemplary embodiment)-   13 rotor element-   14 housing-   15 product inlet-   16 product outlet-   17 fluidization area-   18, 19 conveyor device-   18 conveyor screw-   19 conveyor channel-   20 elevation (baffle element, paddle element, . . . )-   21 gap area-   22 feed vessel-   23 drive motor (for conveyor screw)-   24 drive motor (for rotor element)-   26 dispersing angle-   27, 28 first treatment area (second exemplary embodiment)-   27 curved channel-   27 a first end of 27-   27 b second end of 27-   28 product separator-   29 fluid inlet-   30 fluid outlet-   31, 32, 35 second treatment area (first or second exemplary    embodiment)-   31 first electrode area-   32 second electrode area-   33 first location/collecting area-   34 second location/collecting area-   35 separation vessel-   35 a neck area-   35 b bottom area-   36 partition-   37 voltage source-   38, 39 electric lines

1. A method for separating the various sorts of particles in a mixturecomprised of particles produced by comminuting the grains of cerealgrains, including wheat, and are present as a mixture consisting of atleast a first and second sort of particle, comprising the steps of: a)moving the particles of the first particle sort and the second particlesort of the mixture along at least one surface of at least one solidmaterial in a first impact area in such a way as that at least oneportion of their particle surface is at least sectionally in contactwith the solid material surface as they move along the at least onesolid material surface, as a result of which the particles of the firstparticle sort and the particles of the second particle sort becomeelectrically charged in such a way that the electrical charge of theparticles of the first particle sort differs from the electrical chargeof the particles of the second particle sort enough to enable anelectrostatic separation of particles of the first particle sort fromparticles of the second particle sort; b) in a second impact area,subsequently moving the particles of the first particle sort and secondparticle sort with the sufficiently different electrical charges into anelectrical field between a first electrode area and a second electrodearea, between which there is an electrical potential difference, atessentially the same velocity, as a result of which the particles of thefirst particle sort and second particle sort with the sufficientlydifferent electrical charges move along sufficiently different paths asthey travel through the electrical field; and c) catching the particlesof the first particle sort and the particles of the second particle sortat a first location and at a second location at the end of their journeythrough the electrical field, wherein the at least one surface of the atleast one solid material is concave in the first impact area; andpressing the particles of the first sort and particles of the secondsort in the mixture moving along the concave surface against the concavesurface of the solid material as a result of their centrifugal force asthey move inside the first impact area; and wherein the particles of thefirst sort and the particles of the second sort of the mixture are movedinside the first impact area in the presence of a nonconductive fluid;and wherein the first impact area has a rotor element in a casing, isthe rotor element being shaped in such a way that, when rotated, theparticles of the mixture contained in the first impact area areaccelerated through a surface of the rotating rotor element with aradial and tangential component, and are relayed to a concave innersurface of the casing at a velocity with a radial and tangentialcomponent.
 2. The method according to claim 1, wherein the particles ofthe first particle sort are aleurone particles, and the particles of thesecond particle sort are residual particles from which the aleurone hasbeen removed, in particular shell particles, of the comminuted grain. 3.The method according to claim 1, wherein the solid material iselectrically conductive.
 4. The method according to claim 3, wherein theconductive solid material is grounded.
 5. The method according to claim4, wherein the conductive solid material and one of the electrode areasare additionally interconnected in an electrically conductive manner. 6.The method according to claim 1, wherein the solid material iselectrically nonconductive.
 7. The method according to claim 1, whereinthe surface of the solid material is sectionally electrically conductiveand electrically nonconductive.
 8. The method according to claim 7,wherein the conductive solid material is grounded.
 9. The methodaccording to claim 1, wherein one of the electrode areas is grounded.10. The method according to claim 1, wherein the solid material is ametal or a metal alloy, in particular stainless special steel.
 11. Themethod according to claim 1, wherein the particles of the first sort andthe particles of the second sort of the mixture are moved inside thefirst impact area by means of a fluid stream.
 12. The method accordingto claim 1, wherein the fluid has nitrogen and/or carbon dioxide. 13.The method according to claim 12, wherein the fluid is air.
 14. Themethod according to claim 13, wherein the relative atmospheric moistureof the used air lies under 25%.
 15. The method according to claim 1,wherein the relative velocity between the at least one surface and theparticles moved along it measures about 5 m/s to 25 m/s.
 16. The methodaccording to claim 1, wherein the mixture comprised of the particles hasa humidity content of less than 10%.
 17. The method according to claim1, wherein the particles of the mixture are predominantly smaller than500 μm and preferably larger than 100 μm.
 18. The method according toclaim 1, wherein the first impact area is designed as a kind of cycloneseparator with a fluid inlet, a fluid outlet, a product inlet and aproduct outlet, wherein the mixture having particles of the first sortand particles of the second sort is moved with essentially no electricalcharge through the product inlet, and carried by the fluid streamsupplied through the fluid inlet and discharged through the fluid outletin turbulent motions through the first impact area and along its concavesurface, and finally routed through the product outlet with theparticles in their respective electrically charged state into the secondimpact area.
 19. The method according to claim 1, wherein elevationsproject into a gap area between the rotor element and casing throughwhich passes the moving particle current, and extend from a surface ofthe rotor element and/or from an inner wall of the casing to disperseany agglomerates that might have formed between the particles of themixture.
 20. The method according to claim 1, wherein the first impactarea has a curved channel with a first end and a second end, in which aproduct inlet empties out in the first end, and a product separator witha product outlet and fluid outlet is secured to the second end forseparating the product and fluid, wherein the mixture having particlesof the first sort and particles of the second sort is supplied throughthe product inlet, and carried by a fluid stream supplied through thefluid inlet and discharged through the fluid outlet through the firstimpact area with the curved channel and along its concave surface, andis finally routed through the product separator and its product outletinto the second impact area with the particles in their respectiveelectrically charged state.
 21. The method according to claim 20,wherein the curved channel is a curved hose or bent tube.
 22. The methodaccording to claim 20, wherein the cured channel is spiral or helical.23. The method according to claim 1, wherein the mixture having theelectrically charged particles is discharged from the first impact areainto the second impact area by means of gravitational forces and/orcentrifugal forces and/or a fluid stream.
 24. The method according toclaim 1, wherein agglomerates are formed out of particles of the firstsort or particles of the second sort; and wherein the agglomerates aredispersed before the first impact area or within the first impact area.25. The method according to claim 24, wherein potential agglomerates aredispersed before or within the first impact area through impact.
 26. Themethod according to claim 24, wherein the first impact area is formedvia the series-parallel connection of an impact disperser and a cycloneseparator.